The present invention relates to signal analysis, and more particularly to a method and apparatus for continuous RF signal visualization with high resolution using realtime frequency and time domain displays.
Modern realtime signal analyzers, such as spectrum analyzers and digital oscilloscopes, are capable of acquiring radio frequency (RF) signals at a rate that is too fast for effective realtime display. Current technology takes two basic approaches to addressing this mismatch between realtime signal acquisition and non-realtime signal display. One approach for spectrum analyzers is described in U.S. Pat. No. 5,103,402 entitled “Method and Apparatus for Identifying, Saving and Analyzing Continuous Frequency Domain Data in a Spectrum Analyzer”, issued Apr. 7, 1992 to Steven R. Morton et al. This approach provides for realtime signal acquisition with high signal time resolution, but only a “leisurely”, non-realtime signal display.
A second approach for oscilloscopes is described in U.S. Pat. No. 5,254,983 entitled “Digitally Synthesized Gray Scale for Raster Scan Oscilloscope Displays”, issued Oct. 19, 1993 to David W. Long et al, and U.S. Pat. No. 5,986,637 entitled “Digital Oscilloscope Architecture for Signal Monitoring with Enhanced Duty Cycle”, issued Nov. 16, 1999 to Eric P. Etheridge et al. The second approach addresses the realtime signal display problem by means of data reduction. However these data reduction methods are lossy in the sense that they sacrifice time resolution of the signal for more effective signal visualization. Thus this approach is not appropriate for realtime spectrum analysis.
The '402 patent, referenced above, produced a new three-dimensional (3D) visualization display for RF signals in the frequency domain, commonly called a “spectrogram.” In spectrogram displays time is displayed along a vertical axis, frequency is displayed along a horizontal axis, and power is displayed as a color code. Each spectrum as acquired is displayed as a horizontal trace across the frequency spectrum, with the color of each point along the trace indicating the power of the RF signal at that frequency. The spectrogram display may be displayed in conjunction with a bit map display having a number of the most recently acquired spectrum, as shown in FIG. 1. However each spectrogram trace is displayed in non-realtime, i. e., with time gaps between displayed traces, as indicated above.
What is desired is a realtime signal display for continuous visualization of an RF signal in both the frequency and time domains while maintaining high resolution.